1. Field of Invention
The invention relates to voice detection technology, and more particularly to estimation of noise floors to aid in voice discrimination.
2. Description of Related Art
Voice Activity Detectors (VADs) are an important component in speech coding systems which make use of the natural silence periods in the speech signal to increase transmission efficiency. They are also an essential part of most speech enhancement systems, since in these systems the input noise level and spectral shape are typically measured and updated in only those segments which contain noise only.
VAD information is useful in other applications as well, such as streamlining speech packets on the Internet by compensating for network delays at gaps in speech activity, or detecting end points of speech utterances under noisy conditions in speech recognition tasks.
In most of these applications the background noise is not always stationary. In a hands-free mobile telephone system for instance both car and road noise may change quickly. The VAD therefore has to adapt quickly to the varying noise conditions to provide an accurate indication of noise-only segments. Since the speech signal itself is also not stationary, this task is usually not a simple one. Several VAD algorithms and adaptation methods have been reported in recent years, some of them being part (or in the process of being standardized as part) of standard speech coding systems known in the art. However, these VADs are complicated, and leave room for improvements, both in terms of performance and complexity, particularly for applications other than speech coding.